1. Field of the Invention
This invention relates to a photo-curable liquid silicone rubber composition for forming a templating mother mold adapted to mold a photo-curable liquid resin therein.
2. Prior Art
In a process for developing a new model of automobile part or household appliance, a certain number of products must be produced for the purpose of confirming the outer appearance, shape and performance. To this end, various procedures were developed in the prior art. Among others, a procedure of producing a precision part replica using a mold of silicone rubber, known as a vacuum casting procedure, is widely used in the art. In this procedure, a pattern of molding serving as a master model is prepared from a suitable material such as wood, plastics and metals by manual modeling or by means of a machine tool (which can be controlled on the basis of three-dimensional CAD data). It was recently developed to produce a master model by an optical shaping system of irradiating a UV laser beam to a photo-curable resin in accordance with three-dimensional CAD data inputs. In general, a replica is produced by burying the thus obtained master model in an addition/heat curable liquid silicone rubber composition, curing the silicone rubber composition, removing the master model, casting a thermosetting resin into the cavity in the cured silicone rubber where the master model has been removed, heating the thermosetting resin for curing.
What is desired in the art is to produce such replicas within a short time. Attempts to meet such expectation have been made. For example, JP-A 114711/1991 discloses a method for producing a molded part by introducing a UV-curable liquid resin (epoxy or acrylic reactive resin) into a mold made of a transparent addition room temperature vulcanizable (RTV) silicone rubber composition, and irradiating UV to the liquid resin for curing. To cause the addition RTV liquid silicone rubber composition to cure, however, sufficient control of metering, agitating and curing steps is necessary. In particular, the curing conditions must be strictly controlled in order to increase the dimensional precision of a molded part. The curing usually takes 6 to 24 hours, suggesting that the process is unsatisfactory with respect to the manufacturing time.
An attempt to form a mother mold through photo-curing is disclosed in JP-A 205157/1995. The mold prepared from a photo-curable organic resin is a hard mold, and the resin to be cured in the mold is a conventional thermosetting resin rather than a photo-curable resin.
Therefore, an object of the invention is to provide a photo-curable liquid silicone rubber composition for forming a templating mother mold adapted to form a replica by casting a photo-curable liquid resin therein, the composition allowing the templating mother mold to be formed through simple operation within a short time while the resultant mother mold allowing the photo-curable liquid resin cast therein to be cured with light transmitted by the mother mold.